I just AirPlayed a German film .mp4 with burned English subs to ATV3 with the new update. It worked well!
I don't have an .mp4 or .mov with multi-audio and multi-sub if that is what you are asking about, so I can't test support for that.
Yes thanks i use itunes for aptv 3 and yes i have 2 differen audios with the mp4 and 2 subtitles and audio is 5.1 i just want to be sure before do that because rigth now is working just fine also that true the black mark for subtitles is not any more in the screen